Diamond is one of the most desirable wide bandgap materials for next-generation high-power switching devices, as it has superior physical and electrical properties, including a high breakdown electric field, a high thermal conductivity, and a high carrier mobility. With the developments in large-area, single-crystal diamond substrate growth by high-growth-rate chemical vapor deposition (CVD), there has been a steady advance in diamond device studies. However, due to deep donor energy levels, using nitrogen or phosphorous to achieve n-type doping in diamond has been extremely difficult. As a result, diamond-based electronic devices are mostly based on p-type doped diamond.
N-type doping a (001) diamond substrate with phosphorus has been achieved. However, the resistivity of the n-type layer is still high, owing to the deep phosphorus donor levels. Therefore, although p-n-junction diodes (PNDs) based on diamond have shown a high breakdown voltage, they also have a high on-resistance because the non-ohmic metal/n-type diamond contact and n-type doped diamond layer induce high resistance, which is detrimental to obtaining a high-power, low-loss diode. On the other hand, despite p-type diamond's ability to provide a high breakdown voltage for p-type diamond-based Schottky diodes, there exists a trade-off between on-resistance and breakdown voltage. In order to reduce the resistance of the p-type depletion layer, the acceptor concentration needs to be increased, and the resultant depletion region narrowing results in a decrease of the breakdown voltage. (See, e.g., A. Traore, et al., Zr/oxidized diamond interface for high power Schottky diodes, Appl. Phys. Lett. 104, 052105 (2014).)